Learning interpretable continuous-time models of latent stochastic dynamical systems

We develop an approach to learn an interpretable semi-parametric model of a latent continuous-time stochastic dynamical system, assuming noisy high-dimensional outputs sampled at uneven times. The dynamics are described by a nonlinear stochastic differential equation (SDE) driven by a Wiener process, with a drift evolution function drawn from a Gaussian process (GP) conditioned on a set of learnt fixed points and corresponding local Jacobian matrices. This form yields a flexible nonparametric model of the dynamics, with a representation corresponding directly to the interpretable portraits routinely employed in the study of nonlinear dynamical systems. The learning algorithm combines inference of continuous latent paths underlying observed data with a sparse variational description of the dynamical process. We demonstrate our approach on simulated data from different nonlinear dynamical systems

Co-doped Dy3+ and Pr3+ Ga5Ge20Sb10S65 fibers for mid-infrared broad emission

Rare earth ion doped materials are means to obtain cost-effective infrared light sources, with enough brilliance for applications such as gas sensing. Within a sulfide matrix, the simultaneous luminescence of both Pr3+ and Dy3+ in the Ga5Ge20Sb10S65 glass is reported. The use of these two rare earths is giving rise to a broad continuous luminescence in the 2.2–5.5 µm wavelength range, which could be used as a mid-infrared light source for gas-sensing applications. The demonstration of CO2 and CH4 detection using a fiber drawn from these materials is reported

Aménagement de paysages pour la santé des plantes basé sur des modèles

Partie 3. Vers la conception de paysages agricoles multifonctionnels Chapitre 10National audienc

Ectoparasitosis or Ekbom syndrome?: A case report

International audienc

Modèle Agriconnect un simulateur de paysage couplant modèle agronomique et modèle écologique

Modèle Agriconnect un simulateur de paysage couplant modèle agronomique et modèle écologique. Séminaire PAYOT

Mid-Infared sources based on rare-earth-doped chalcogenide glass waveguides

International audienceVitreous materials based on chalcogen elements (S, Se, Te) show large transparency windows that extend from the visible up to 12-15 µm in the infrared, depending on their compositions. This is due to the lower phonon energies of chalcogenides, which are also responsible for enhanced luminescence of rare-earth ions embedded in such matrices. As a result, they possess a high potential for applications as infrared sources, where rare-earth-doped oxide glasses cannot operate. As far as shaping is concerned, specific chalcogenide glass compositions can be obtained in the form of optical fibers, thin films or planar waveguides. The presentation deals with the latest results in terms of mid-infrared luminescence of Pr3+, Nd3+, Tb3+, Dy3+, and Er3+ ions in chalcogenide glasses, optical fibers, and micro-waveguides

Modélisation de paysages agricoles pour la simulation et l'analyse de processus

International audienc

Modélisation de paysages agricoles pour la simulation et l'analyse de processus

International audienc

Modélisation de paysages agricoles pour la simulation et l'analyse de processus

International audienc

Multi-scale approach to biodiversity proxies of biological control service in European farmlands

Intensive agriculture has profoundly altered biodiversity and trophic relationships in agricultural landscapes, leading to the deterioration of many ecosystem services such as pollination or biological control. Information on which spatio-temporal factors are simultaneously affecting crop pests and their natural enemies is required to improve conservation biological control practices. We conducted a study in 80 winter wheat crop fields distributed in three regions of North-western Europe (Brittany, Hauts-de-France and Wallonia), along intra-regional gradients of landscape complexity. Five taxa of major crop pests (aphids and slugs) and natural enemies (spiders, carabids, and parasitoids) were sampled three times a year, for two consecutive years. We analysed the influence of regional (meteorology), landscape (structure in both the years n and n-1) and local factors (hedge or grass strip field boundaries, and distance to boundary) on the abundance and species richness of crop-dwelling organisms, as proxies of the service/disservice they provide. Firstly, there was higher biocontrol potential in areas with mild winter climatic conditions. Secondly, natural enemy communities were less diverse and had lower abundances in landscapes with high crop and wooded continuities (sum of interconnected crop or wood surfaces), contrary to slugs and aphids. Finally, field boundaries with grass strips were more favourable to spiders and carabids than boundaries formed by hedges, while the opposite was found for crop pests, with the latter being less abundant towards the centre of the fields. We also revealed temporal modulation—and sometimes reversion—of the impact of local elements on crop biodiversity. To some extent, these results are quite unexpected and cause controversy because they show that hedgerows and woodlots should not be the unique cornerstones of agro-ecological landscape design strategies. We point out that combining woody and grassy habitats to take full advantage of the features and ecosystem services they both provide (biological pest control, windbreak effect, soil stabilization) may promote sustainable agricultural ecosystems. It may be possible to both reduce pest pressure and promote natural enemies by accounting for taxa-specific antagonistic responses to multi-scale environmental characteristics